1. The Field of the Invention
The present invention relates generally to irrigation control systems, and more particularly, but not necessarily entirely, to systems that utilize weather data for irrigation control.
2. Description of Background Art
Water conservation is a major issue in many parts of the world. In particular, population growth is putting fresh water supplies under tremendous strain. Notably, landscape water usage consumes more than half of the potable water supplies in some areas. Landscape water usage refers to the artificial application of water to promote the growth of desired plants. This is especially true in agricultural areas where crops require frequent watering in order to achieve maximum yield. However, residential, governmental and commercial water usage also significantly taps the available water supply, i.e., yards, golf courses, and parks also demand significant amounts of water to maintain healthy foliage.
A well known device to conserve and apply water during landscape watering is an irrigation system which controls the application of the water. A typical irrigation system comprises an irrigation controller, valves, pipes, and sprinkling heads. The irrigation controller, customarily also known as a clock or timer, automatically regulates the opening and the closing of the valves. The valves allow water to pass into the pipes and out of the sprinkling heads thereby irrigating the desired location. Properly configured, an irrigation controller can achieve some conservation of water. Irrigation controllers are commonly employed in the agricultural, commercial, governmental and residential settings albeit the scale of the operation can vary dramatically. The irrigation controller is often set to water “automatically” on preset days and times. Thus, the user can at least be assured that the watering occurs so that at least a predetermined amount of water is dispensed but often without any adjustment being made if a reduced amount of water would be optimum.
One great disadvantage to using an irrigation controller preset to water at specified days and times is the inability to automatically adjust for changing water requirements of the landscape. For example, during a rainy period, many previously available irrigation controllers still water even though no watering may be needed due to rainfall. Likewise, during a hot and windy period, additional water may be needed but because of the preset schedule, it is not provided. Also, because of the changing seasons in many areas, one preset watering schedule usually will not effectively water the landscape over a period of several months, i.e., less water may be needed in the spring than the hot summer months.
Furthermore, because the lack of water is potentially more harmful than too much water (except in the extreme case), the previously available irrigation controllers are typically programmed to “over water” to provide a margin of safety to the landscape and avoid death of the landscape due to dehydration. While this ensures that the landscape has sufficient water to maintain a viable landscape, it commonly results in wasteful water consumption.
In order to overcome the aforementioned problems, recently developed irrigation controllers are capable of receiving electronic input to improve the watering of the landscape based upon the estimated water needs of the landscape. The water requirement for the landscape can be determined through several methods, including visual inspection, soil moisture sensors, evaporative pan measurements or by calculating the evapotranspiration. Evapotranspiration is the most popular method for determining the water needs of the landscape.
Evapotranspiration is defined as the water lost to the atmosphere by two processes-evaporation and transpiration. Evaporation is the loss from open bodies of water, such as lakes and reservoirs, wetlands, bare soil, and snow cover; transpiration is the loss of water from living-plant surfaces. Several factors other than the physical characteristics of the water, soil, snow, and plant surface also affect the evapotranspiration process. The more important factors which impact evapotranspiration include net solar radiation, relative humidity, wind speed, density and type of vegetative cover, availability of soil moisture, elevation above sea level, reflective land-surface characteristics, and season of year. Because of the importance of solar energy to evapotranspiration, the evapotranspiration which is actually experienced also varies with latitude, season of year, time of day, and cloud cover. Evapotranspiration is typically expressed in either millimeters or inches of water per hour, per day or week.
The seasonal variability in evapotranspiration differs greatly and is similar to the seasonal trend in air temperature. Daily fluctuations in evapotranspiration can also occur. On clear days, the rate of transpiration increases rapidly in the morning and reaches a maximum usually in early afternoon or midafternoon. The midday warmth can cause closure of plant stomata, which results in a decrease in transpiration.
Numerous formulas have been developed, tested and refined over the years to calculate evapotranspiration. The formulas typically have been developed to reference either alfalfa or cool-season turf grass. To adapt the results to a specific plant, the reference value is modified by a crop coefficient. Each crop has its own crop coefficient curve, which is based upon plant physiology, height, density and growth stage. Research is ongoing to provide crop coefficient data for various crops and seasonal changes. The estimated potential evapotranspiration may differ from actual evapotranspiration based on water stress of the plants, and based on the margin of error of the model or equation used for the estimate.
Due to the large number of evapotranspiration equations in use today, the Evapotranspiration in Hydrology and Irrigation Committee of the American Society of Civil Engineers developed the “Standardized Reference Evapotranspiration Equation.” Two equations were actually developed, one for short clipped grass and the other for tall crop. The landscape industry has also generally accepted a formula referred to as the FAO Penman-Monteith equation as a reliable means of calculating the potential evapotranspiration. Further information regarding evapotranspiration and the FAO Penman-Monteith equation can be found in Crop Evapotranspiration: Guidelines for Computing Crop Water Requirements published by Food & Agriculture Organization of the United States (June 2000) and also located at http://www.fao.org on the internet, both of which are hereby incorporated by reference in their entirety. It should be noted that as used herein, the term evapotranspiration refers to the actual evapotranspiration or the potential evapotranspiration determined from any of the methodologies now known or may become known in the future. Other methodologies, without limitation, include the Blaney-Criddle, radiation, and pan evaporation methods.
Most estimates of evapotranspiration are derived from studies of areas where climate, available moisture, and plant cover are relatively uniform. In order to calculate evapotranspiration for an area, a weather station collects data that can be used in the equation. For example, temperature, wind, solar-radiation and humidity values are collected and logged hourly by the weather station and are retrieved by a computer. The evapotranspiration can then be used to determine if an adjustment to the preset water schedule is warranted.
Once the evapotranspiration has been calculated, a crop coefficient is used to modify the reference evapotranspiration to reflect the water use of a particular plant or group of plants particularly with reference to the plant species. In some areas, the crop coefficient values changes seasonally.
One major problem with the previously available systems is that once the evapotranspiration has been calculated for an area based upon the measurements obtained from a weather station, the irrigation controllers must still be adjusted based upon that information. This is problematic because the irrigation controller may be located some distance from the weather station or central control computer where the evapotranspiration was initially calculated. Placing a weather station and computer to calculate the evapotranspiration near each irrigation controller is cost prohibitive in all but a few cases.
An attempt to overcome this drawback has been developed to utilize two-way communications, an on-site water manager, and an operator to monitor every irrigation controller. The operator communicates to a water manager by radio or cell phone the required information obtained from a weather station to adjust the watering schedule. The water manager can then make the appropriate adjustments to the irrigation controller. It has been recognized that the need for human intervention has prevented implementation of such systems on a wide scale basis.
Another attempt to overcome the aforementioned drawbacks, utilizes the step of having a user manually phone a commercial radio paging station to generate a paging signal for transmission to a receiver connected to a specific irrigation controller. The user first obtains the weather data and calculates the evapotranspiration to determine the appropriate adjustment to the watering schedule. Once the paging signal has been received by the receiver, it interfaces with the irrigation controller to control the watering schedule. A problem with this system is that the user of the system must manually call the paging station to send a signal to control the irrigation system. Further, each irrigation controller has a separate paging number, thereby requiring a separate call and page for each irrigation controller. Again, the described system disadvantageously requires intervention by a human and is therefore not fully automated.
In still another attempt to overcome the aforementioned drawbacks, coded evapotranspiration values and corresponding evapotranspiration zones are broadcast to a collection of microprocessor-based irrigation sprinkler controllers located within a geographic area. The controllers produce an adjustment value responsive to the evapotranspiration data which is broadcast for a particular zone. However, this particular system calculates the evapotranspiration values at one location prior to broadcasting, and only the evapotranspiration data and evapotranspiration zones data are broadcast. Thus, each irrigation site receives weather data which may be, or may not be, applicable to the location of a particular irrigation site. This previously available system still is disadvantageous because each site may have distinct characteristics from the other sites and the application of evapotranspiration zone data may be inapplicable to the location of that particular irrigation site.
In view of the foregoing, it will be appreciated that the previously available systems are characterized by significant drawbacks and disadvantages. For example, the decision to irrigate is made at the central computer and not on-site providing inaccurate watering. In addition, the previously available systems do not transmit the weather data but only evapotranspiration values calculated by the central computer which prevents on-site adjustments from being made. Thus, it would be a great advance in the art to provide a system and method which overcomes the aforementioned drawbacks and disadvantages.